1. Field of the Invention
The present invention relates generally to quality control systems and more particularly to a concentricity test fixture for helical springs and similar resilient members, and to a technique for assuring that a lot of such resilient members exhibits acceptable compressive attributes such as squareness of the ends under a load.
2. Description of the Related Art
It is desirable to monitor coil spring quality by checking for departure from a helical configuration and fixtures for accomplishing this for springs in their unstressed state is well documented. For example, U.S. Pat. No. 4,472,882 discloses a test fixture for measuring the squareness of unstressed coil springs by positioning a candidate spring adjacent a calibrated contoured surface of unique geometry and positioning the spring to touch the fixture at various locations. The patented arrangement does not address variations in spring squareness which might occur when the spring is compressed or stretched.
Departure from a truly helical configuration under load can have adverse effects. For example, in a mechanism having coil spring loaded poppet valves, excess departure can side-load the valve train increasing friction, affecting performance and decreasing wear life. The ability to test a coil spring or similar resilient member for squareness under load is a salient feature of the present invention.